MC68020 Motorola, MC68020 Datasheet - Page 163

• Manufacturer Part Number: MC68020
• Description: (MC68020 / MC68EC020) MICROPROCESSORS USERS MANUAL
• Manufacturer: Motorola

7.2.2 Coprocessor Conditional Instructions
The conditional instruction category provides program control based on the operations of
the coprocessor. The coprocessor evaluates a condition and returns a true/false indicator
to the main processor. The main processor completes the execution of the instruction
based on this true/false condition indicator.
The implementation of instructions in the conditional category promotes efficient use of
both the main processor and the coprocessor hardware. The condition specified for the
instruction is related to the coprocessor operation and is therefore evaluated by the
coprocessor. However, the instruction completion following the condition evaluation is
directly related to the operation of the main processor. The main processor performs the
change of flow, the setting of a byte, or the TRAP operation, since its architecture explicitly
implements these operations for its instruction set.
Figure 7-8 shows the protocol for a conditional category coprocessor instruction. The main
processor initiates execution of an instruction in this category by writing a condition
selector to the condition CIR. The coprocessor decodes the condition selector to
determine the condition to evaluate. The coprocessor can use response primitives to
request that the main processor provide services required for the condition evaluation.
7-10
(SEE NOTE 1)
M1
OPERATION WORD
M2
COMMAND CIR
M3
FROM RESPONSE CIR
1) PERFORM SERVICE REQUESTED BY RESPONSE
PRIMITIVE
2) IF (COPROCESSOR RESPONSE PRIMITIVE
INDICATES "COME AGAIN") GO TO M3
M4
(SEE NOTE 2)
NOTES: 1. "Come Again" indicates that further service of the main processor is being requested by the coprocessor.
RECOGNIZE COPROCESSOR INSTRUCTION F-LINE
WRITE COPROCESSOR COMMAND WORD TO
READ COPROCESSOR RESPONSE PRIMITIVE CODE
PROCEED WITH EXECUTION OF NEXT INSTRUCTION
2. The next instruction should be the operation word pointed to by the ScanPC at this point. The operation of
the MC68020/EC020 ScanPC is discussed in
MAIN PROCESSOR
Figure 7-7. Coprocessor Interface Protocol
for General Category Instructions
M68020 USER’S MANUAL
7.4.1 ScanPC.
C1
COMMAND EXECUTION
C2
DO STEPS 1) AND 2) BELOW
1) REQUEST SERVICE BY PLACING APPROPRIATE
2) RECEIVE SERVICE FROM MAIN PROCESSOR
C3
C4
C5
RESPONSE CIR
DECODE COMMAND WORD AND INITIATE
WHILE (MAIN PROCESSOR SERVICE IS REQUIRED)
REFLECT "NO COME AGAIN" IN RESPONSE CIR
COMPLETE COMMAND EXECUTION
REFLECT "PROCESSING FINISHED" STATUS IN
RESPONSE PRIMITIVE CODE IN RESPONSE CIR
COPROCESSOR
MOTOROLA